Electro hydraulic servo valve

ABSTRACT

An electro hydraulic servo valve having a nozzle tube movable in accordance with an electrical signal and a spool movable in accordance with differential pressure produced through the nozzle tube to meter a variable volume of hydraulic fluid through the valve and means including an abutment for restricting or changing the movement of the nozzle tube relative to the applied electric signal during movement thereof to provide the electro hydraulic servo valve with a variable gain characteristic in that the spool follows the movement of the nozzle tube in one proportion before the nozzle tube engages the abutment and in another proportion after the nozzle tube engages the abutment.

United States Patent Ericson 1*Sept. 12, 1972 [54] ELECTRO HYDRAULIC SERVO VALVE [56] References Cited [72] Inventor: Donald W. Ericson, 185 Westwood UNITED STATES PATENTS Birmingham, Mich- 4809 3,473,548 10/1969 Ericson et al. ....137/625.62 x

[ Notice: The portion of the term of this Primary Examiner-Henry T. Klinksiek patent subsequent to Oct. 21, 1986, i has been disclaimed Att0rneyWhittemore, Hulbert & Belknap [22] Filed: Sept. 8, 1970 [57] ABSTRACT [21.] Appl. No.: 70,594 An electro hydraulic servo valve having a nozzle tube movable in accordance with an electrical signal and a Related US. Application Data spool movable in accordance with differential pressure produced through the nozzle tube to meter a variable [63] Contmuanon of 636910 May volume of hydraulic fluid through the valve and means 1967, aband including an abutment for restricting or changing the movement of the nozzle tube relative to the applied [52] US. Cl ..l37/625.62 electric Signal during movement thereof to provide the Int. Clelectro hydraulic servo valve a variable [58] Field Of Search ..137/8l-85, 625.61, characteristic in that the spool follows the movement UTILIZING DEVICE of the nozzle tube in one proportion before the nozzle tube engages the abutment and in another proportion after the nozzle tube engages the abutment.

16 Claims, 4 Drawing Figures HYDRAULIC FLUID PATENTEU 12 3.690.345

HYDRAULIC FLUID UTILIZING DEVICE FIG.I

H62 FIG.4

, FLAPPER MOVEMENT X FLAPPER MOVEMENT FLUID FLOW FLUID FLOW INVENTOR DONALD W. ERICSON ATTORNEYS ELECTRO HYDRAULIC SERVO VALVE This application is a continuation of application Ser. No. 636,910, filed May 8, 1967 and now abandoned.

BACKGROUND OF THE INVENTION The invention relates to electro hydraulic servo valves wherein flow of hydraulic fluid is controlled in accordance with an electrical signal and relates more particularly to electro hydraulic servo valves wherein a nozzle tube is caused to move in accordance with the movement of a flapper valve positioned by an electrical signal and a spool for metering hydraulic fluid is caused to move in accordance with differential pressure produced on the movement of the nozzle tube.

In the past where such electro hydraulic servo valves have been known the ratio of movement between the nozzle tube and spool has usually been fixed in accordance with the physical dimensions of the valve members including the nozzle tube and spool. Further, in such prior electro hydraulic servo valves there has been no simple, economical and efficient means for providing a dual gain characteristic for the servo valve.

That is to say, it has been difficult in the past to change the gain of the servo valve at a selected point in the operation thereof.

Since electro hydraulic servo valves are used primarily for controlling movements which are often most economical and efficient if controlled at different speeds, a simple, economical and efficient multiple gain electro hydraulic servo valve is desirable. This is true, for example, in the controlling of machine tools where movement of a tool into proximity with work could be accomplished relatively fast while the actual machining must be accomplished during a relatively slow advance of the tool toward the work.

SUMMARY OF THE INVENTION In accordance with the invention there is provided an electro hydraulic servo valve of the type wherein a nozzle tube is moved in accordance with movement of a flapper valve through a force motor and an electrical signal applied to the force motor. The nozzle tube moves a spool, which actually meters hydraulic fluid through the valve in accordance with a differential pressure created by movement of the nozzle tube, and means are provided for limiting or changing the movement of the nozzle tube relative to movement of the flapper within the range of movement of the nozzle tube without correspondingly limiting or changing the movement of the spool. Thus in accordance with the invention an especially simple, economical and efiicient electro hydraulic servo valve is provided which has a multiple gain characteristic and in which the gain characteristic can be tailored to a job requirement.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal cross section of an electro hydraulic servo valve constructed in accordance with the invention.

FIG. 2 is a graph illustrating the gain characteristics of the electro hydraulic servo valve of FIG. 1.

FIG. 3 is an enlarged partial cross section of a modification of the electro hydraulic servo valve illustrated in FIG. 1.

FIG. 4 is a graph illustrating the gain characteristic of the modified electro hydraulic servovalve illustrated in FIG. 3. 1

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electro hydraulic servo valve 10 illustrated in FIG. 1 is connected to a source of hydraulic fluid l2 and a utilizing device 14. In operation the electro hydraulic servo valve 10 is provided to meter hydraulic fluid from the hydraulic fluid source 12 to the utilizing device 14 in accordance with an electrical signal fed to the servo valve 10 over the conductors l6 and 18.

The electro hydraulic servo valve 10 includes the force motor mechanism 20 and the valve mechanism 22. The force motor mechanism 20 includes the housing 24, the electric force motor 26 and the flapper 28. I

In operation, as with prior .known electro hydraulic servo valves, the force motor mechanism 20 operates to move the end 29 of flapper 28 a distance relative to the nozzles 30 and 32 of the pilot or nozzle tube 34 of the valve mechanism 22 a distance proportional to the magnitude of the electrical signal fed to the force motor 26 through conductors 16 and 18.

The valve mechanism 22 includes the cylindrical body 36, end caps 38 and 40, nozzle tube 34 and spool 42. In addition the valve mechanism 22 includes the annular abutment means 44 and 46 at opposite ends of the cylindrical body 36.

Further, in accordance with commonly owned US. Pat. No. 3,473,548, the valve mechanism 22 includes the springs 48 and 50 and the springs 52 and 54 connected between the adjusting screws 56 and 58, the opposite ends of the nozzle tube 34, and the opposite ends of the spool 42, as shown.

In addition in accordance with the present invention adjustable abutment screws 60 and 62 are provided extending through the end caps 38 and 40. The adjustable abutment screws 60 and 62 are positioned to engage the nozzle tube 34 in its movement left or right in FIG. 1, as will be seen subsequently.

In operation of the valve mechanism 22 hydraulic fluid from the hydraulic fluid source 12 is metered through conduit 64 into passage 66 in the cylindrical body member 36 and passes into the end chambers 68 and 70 and into the annular chambers 72 and 74 formed by the annular grooves 76 and 78 in the spool 42. The hydraulic fluid from the end chambers 68 and 70 passes through the orifices 80 and 82 in the opposite ends of the nozzle tube 34 through the transverse passages 84 and 86 in the nozzle tube and the aligned transverse passages 88 and 90 in the spool 42 into the annular chambers 92 and 94 formed between the annular abutment means 44 and 46 and the spool 42. The hydraulic fluid flows through the passages 96 and 98 in the cylindrical body member 36 through the transverse openings 100 and 102 in the spool and the aligned openings 104 and 106 into the inner portions of the opposite ends of the nozzle tube adjacent the nozzles 30 and 32, respectively. The hydraulic fluid then passes out of the nozzles 30 and 32, past the end 29 of the flapper 28, into the hydraulic fluid return chamber 108 and through passages 110 in the cylindrical body member and back to the hydraulic fluid source through the conduit 112.

The differential pressure thus developed at the opposite ends of the nozzle tube will depend on the flow of hydraulic fluid through the orifices 80 and 82 which is controlled by the flow of fluid through the nozzles 30 and 32, respectively. Thus with the end 29 of flapper 28 moved toward one of the nozzles 30 or 32 to restrict that nozzle and open the other nozzle a differential pressure will develop which is proportional to the movement of the flapper 28 and thus proportional to the electric signal applied to the force motor to initially produce a movement of the nozzle tube proportional to the applied electrical signal. In accordance with the spring rates of the springs 48 and 50 and 52 and 54 as set forth in the above referenced patent application, the spool 42 will amplify the movement of the nozzle tube 34 and will be moved in accordance with the pressures in the chambers 92 and 94. Thus metering of hydraulic fluid by the spool 42 will be proportional to the movement of the flapper 28 and thus proportional to the magnitude of the electricalsignal supplied over conductors 16 and 18.

Further, the movement of the spool would be constant over the entire range of movement of the nozzle tube and flapper valve of prior constructions. Thus with prior valve constructions valve control to provide a high gain for rapid traverse and to provide a low gain for fine adjustment in machining for example-is not possible. I

However in accordance with the present invention, as shown in FIG. 1, the nozzle tube is limited in movement after an abutment screw 60 or 62 is contacted to prevent further movement of the nozzle tube in response to further movement of the flapper 28. After the nozzle tube 34 is stopped, the spool 42 may be caused to move to its limiting position with the rage of spool movement being determined by the positioning of the flapper 28, which after stopping of the nozzle tube 34 provides additional restriction or opening of the nozzles 30 and 32 to increase the pressure in one of the chambers 92 and 94 and decrease the pressure in the other chamber, as will be readily apparent from the operation of such electro hydraulic servo valves.

' Thus, as shown in FIG. 2, wherein hydraulic fluid I flow or spool movement is plotted in the Y direction and flapper movement is plotted in the X direction, it will be seen that on movement of the flapper 28 initially, the rate of flow or spool displacement is proportional to flapper movement. However, on the nozzle tube 34 contacting an abutment 60 or 62 Without further movement of the flapper, the spool 42 will be moved to its limit in the direction considered to provide a substantially infinite gain for the electro hydraulic servo valve after the nozzle 34 engages the abutment screw 60 or 62.

A modification of the invention is illustrated in FIG. 3. Thus in FIG. 3 the adjusting screws 60 and 62 have been replaced by adjusting screws 114 which receive the plunger abutment 116 in the hollow outer end 118. The plunger 116 is prevented from movement completely out of the adjusting screw 114 by convenient means, such as pin 120 reciprocally mounted in the slot 122. Plunger 116 is urged outwardly of the respective adjusting screws 114 by means of springs 124, as shown.

In use the plunger 116 is initially out of contact with the nozzle tube 126 whereby a first gain, as shown in FIG. 4, is achieved by the modified electro hydraulic servo valve 128 which except for the modification of the adjusting screws and 62 in FIG. 1 is exactly the same as the electro hydraulic servo valve 10 of FIG. 1. On the nozzle tube 126 contacting a plunger abutment 116 at either end thereof the movement of the nozzle tube is restricted so that additional movement of the flapper of the servo valve 128 will cause proportionally less movement of the nozzle tube 34 while the pressures created on the spool of the modified electro hydraulic servo valve will be increased and decreased at opposite ends to provide a second gain ratio for the fluid flow again plotted along the Y axis in FIG. 4 relative to flapper movement plotted along the X axis in FIG. 4.

From the embodiments of the invention set forth in detail it will be readily understood that the gain of the electro hydraulic servo valve 10 may be varied at any point and may be varied as desired. Thus, for example, the abutments 60 and 62 of the electro hydraulic servo valve 10 may be used in conjunction with an earlier contacted biased abutment, such as the abutment plunger 116 of electro hydraulic servo valve 128 to provide two gain ratios and an infinite gain for an electro hydraulic servo valve if desired. Alternatively multiple biased abutments contacting the nozzle valve at different times may be used together or different abutment means may be provided at the opposite ends of the nozzle tube to provide any desired gain characteristics for an electro hydraulicservo valve, such as that illustrated in FIG. 1.

What I claim as my invention is:

1. An electro hydraulic servo valve including a pilot member, means operably associated with the pilot member for moving the pilot member in proportion to an electric signal applied to the valve, a metering member operably associated with the pilot member and at least initially responsive to movement thereof to move in accordance with the movement of the pilot member and means operably associated with the pilot member for changing the relative movement of the metering member and pilot member at some point in the movement of the pilot member to provide a variable gain servo valve.

2. Structure as set forth in claim 1 wherein the means for changing the relative movement to provide a variable gain comprises an abutment engageable with the pilot member during movement thereof.

3. Structure as set forth in claim 2 and further including means operably associated with the abutment for adjusting the position of the abutment relative to the pilot member.

4. Structure as set forth in claim 3 wherein the abutment is a solid abutment.

5. Structure as set forth in claim 3 wherein the abutment is a resilient abutment.

6. Structure as set forth in claim 1 wherein the pilot member is a nozzle tube.

7. Structure as set forth in claim 6 wherein the metering member is a spool surrounding the nozzle tube.

8. Structure as set forth in claim 7 and further including resilient means connected between the nozzle tube and a relatively fixed abutment and between the nozzle tube and spool.

9. Structure as set forth in claim 8 wherein the resilient means have different spring rates.

10. Structure as set forth in claim 8 wherein the position of the abutment is adjustable.

11. in electro hydraulic servo valve structure including a body member, a spool reciprocably mounted in the body member, a nozzle tube reciprocably mounted in the spool, a force motor mounted on the body member having a metering member operably associated with and movable relative to the nozzle tube and hydraulic fluid means operably associated with the body member, spool and nozzle tube for moving the spool in response to movement of the nonle tube in accordance with movement of the force motor metering member relative thereto to meter hydraulic fluid through said valve, an abutment secured to the body member and engageable with the nozzle tube for varying the movement thereof in response to movement of the force motor metering member to provide a variable gain servo valve.

12. Structure as set forth in claim 11 and further including means operably associated with the abutment for adjusting the abutment.

13. Structure as set forth in claim 11 wherein the abutment is resilient.

14. Structure as set forth in claim 11 and further including resilient means operable between the body member and nozzle tube and between the body member and nozzle tube and between the nozzle tube and spool.

15. Structure as set forth in claim 14, wherein the resilient means are springs and the spring rates of the springs are different.

16. An electro hydraulic servo valve comprising a body member having an extending opening therethrough, a spool reciprocably mounted within the opening in the body member, a nozzle tube mounted in the spool for reciprocal movement relative thereto axially thereof, an annular abutment in each end of the opening through the body member limiting the movement of the spool therein, a source of hydraulic fluid, fluid passages extending from the source of hydraulic fluid through the body member, through an outer portion of one end of the nozzle tube, between the spool and the annular abutment adjacent the one end of the nozzle tube, through an inner portion of the other end of the nozzle tube, between the spool and the annular abutment adjacent the other end of the nozzle tube, through an inner portion of the other end of the nozzle tube and through nozzles at the inner end of the inner portion of both ends of the nozzle tube intoa hydraulic return to the source of hydraulic fluid, a force motor having a flapper valve operably associated with the nozzles of the nozzle tube for metering the flow of hydraulic fluid through the nozzles in accordance with the position of the force motor flapper valve and 

1. An electro hydraulic servo valve including a pilot member, means operably associated with the pilot member for moving the pilot member in proportion to an electric signal applied to the valve, a metering member operably associated with the pilot member and at least initially responsive to movement thereof to move in accordance with the movement of the pilot member and means operably associated with the pilot member for changing the relative movement of the metering member and pilot member at some point in the movement of the pilot member to provide a variable gain servo valve.
 2. Structure as set forth in claim 1 wherein the means for changing the relative movement to provide a variable gain comprises an abutment engageable with the pilot member during movement thereof.
 3. Structure as set forth in claim 2 and further including means operably associated with the abutment for adjusting the position of the abutment relative to the pilot member.
 4. Structure as set forth in claim 3 wherein the abutment is a solid abutment.
 5. Structure as set forth in claim 3 wherein the abutment is a resilient abutment.
 6. Structure as set forth in claim 1 wherein the pilot member is a nozzle tube.
 7. Structure as set forth in claim 6 wherein the metering member is a spool surrounding the nozzle tube.
 8. Structure as set forth in claim 7 and further including resilient means connected between the nozzle tube and a relatively fixed abutment and between the nozzle tube and spool.
 9. Structure as set forth in claim 8 wherein the resilient means have different spring rates.
 10. Structure as set forth in claim 8 wherein the position of the abutment is adjustable.
 11. In electro hydraulic servo valve structure including a body member, a spool reciprocably mounted in the body member, a nozzle tube reciprocably mounted in the spool, a force motor mounted on the body member having a metering member operably associated with and movable relative to the nozzle tube and hydraulic fluid means operably associated with the body member, spool and nozzle tube for moving the spool in response to movement of the nozzle tube in accordance with movement of the force motor metering member relative thereto to meter hydraulic fluid through said valve, an abutment secured to the body member and engageable with the nozzle tube for varying the movement thereof in response to movement of the force motor metering member to provide a variable gain servo valve.
 12. Structure as set forth in claim 11 and further including means operably associated with the abutment for adjusting the abutment.
 13. Structure as set forth in claim 11 wherein the abutment is resilient.
 14. Structure as set forth in claim 11 and further including resilient means operable between the body member and nozzle tube and between the body member and nozzle tube and between the nozzle tube and spool.
 15. Structure as set forth in claim 14, wherein the resilient means are springs and the spring rates of the springs are different.
 16. An electro hydraulic servo valve comprising a body member having an extending opening therethrough, a spool reciprocably mounted within the opening in the body member, a nozzle tube mounted in the spool for reciprocal movement relative thereto axially thereof, an annular abutment in each end of the opening through the body member limiting the movement of the spool therein, a source of hydraulic fluid, fluid passages extending from the source of hydraulic fluid through the body member, through an outer portion of one end of the nozzle tube, between the spool and the annular abutment adjacEnt the one end of the nozzle tube, through an inner portion of the other end of the nozzle tube, between the spool and the annular abutment adjacent the other end of the nozzle tube, through an inner portion of the other end of the nozzle tube and through nozzles at the inner end of the inner portion of both ends of the nozzle tube into a hydraulic return to the source of hydraulic fluid, a force motor having a flapper valve operably associated with the nozzles of the nozzle tube for metering the flow of hydraulic fluid through the nozzles in accordance with the position of the force motor flapper valve and providing a differential pressure between the abutments and spool to provide movement of the spool in accordance with movement of the nozzle tube, end caps secured over the opposite ends of the opening through the body member and abutment means adjustably secured to at least one of the end caps for restricting movement of the nozzle tube after an initial movement thereof thereby varying the relative movement of the spool relative to the nozzle tube in response to movement of the flapper and providing a servo valve variable gain characteristic. 